Synthesis and characterization of optically active Schiff base complexes of the lanthanides

The complexes formed upon the addition of Eu3+ to chiral Schiff base ligands derived from salicylaldehyde have been characterized in the solid state and in solution using techniques associated with luminescence spectroscopy. At 70K, these complexes contain Eu3+ ions in low symmetry, as indicated by the appearance of a minimal number of luminescence bands associated with the 5D0 → 7F/sub J/ f-f transitions. These data together with the analytical data suggest that these complexes are polymeric with 1:1 Eu/ligand stoichiometries. The overall optical activity associated with these complexes was characterized using Circularly Polarized Luminescence (CPL) spectroscopy. These results indicate that the primary sources of optical activity in the Eu3+ luminescence spectra are due to conformational effects of the bound ligands. There is no correlation between the magnitude of the g/sub lum/ values with the absolute configurations of the chiral centers in the ligands. However, the signs of the CPL bands do change with the nature of the conformational processes around the Eu3+ atom. A sum of conformational effects has been successfully characterized in complexes with more than one chiral center, since the CPL spectra show more than one band in both the 0 → 1 and 0 → 2 regions. It is certain that the changes witnessed in the CPL spectra are due to changes in the polymeric structure of these complexes. This study verifies that CPL spectroscopy continues to aid in the development of spectra-structure correlations in the excited state